Systems and methods for asynchronous re-modulation with adaptive I/Q adjustment

ABSTRACT

Various embodiments provide for systems and methods for signal conversion of one modulated signal to another modulated signal using demodulation and then re-modulation. According to some embodiments, a signal receiving system may comprise an I/Q demodulator that demodulates a first modulated signal to an in-phase (“I”) signal and a quadrature (“Q”) signal, an I/Q signal adjustor that adaptively adjusts the Q signal to increase the signal-to-noise ratio (SNR) of a transitory signal that is based on a second modulated signal, and an I/Q modulator that modulates the I signal and the adjusted Q signal to the second modulated signal. To increase the SNR, the Q signal may be adjusted based on a calculated error determined for the transitory signal during demodulation by a demodulator downstream from the I/Q modulator.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/506,452 filed Oct. 3, 2014 and entitled “Systems and Methodsfor Asynchronous Re-Modulation with Adaptive I/Q Adjustment,” now U.S.Pat. No. 9,813,198, which is a divisional of U.S. patent applicationSer. No. 14/155,211 filed Jan. 14, 2014 and entitled “Systems andMethods for Asynchronous Re-modulation with Adaptive I/Q Adjustment,”now U.S. Pat. No. 9,077,425, which is a continuation of U.S. patentapplication Ser. No. 13/627,996 filed Sep. 26, 2012 and entitled“Systems and Methods for Asynchronous Re-modulation with Adaptive I/QAdjustment,” now U.S. Pat. No. 8,630,600, which claims the benefit ofU.S. Provisional Patent Application Ser. No. 61/539,341 filed Sep. 26,2011 and entitled “Method and Apparatus for Non-Synchronous Remodulatorof Zero IF Receiver with Adaptive I/Q Gain Control,” each of which isincorporated by reference herein.

FIELD OF THE INVENTION(S)

The present invention(s) relate to receiving signals and, moreparticularly, to demodulating and modulating signals.

BACKGROUND

Signal modulation plays a key role in many electronic applications,especially those relating to communications where modulation techniquesfacilitate transmitting and receiving wired and wireless communicationsignals. Use of modulation techniques is common not only incommunications over coaxial cable and twisted pair cables, but also inover-the-air communications at microwave and satellite frequencies.Typically, several stages of signal modulation are involved intransmitting a communications signal from one location and receiving thecommunications signal at another location. This is often the case formicrowave communications, where it can be necessary to transmit acommunications signal from a remote site to a local office using amicrowave communications system, and then transmit the communicationssignal from the local office to customer premise equipment (CPE) over acable.

Traditional signal receivers, particularly those configured to receivewireless signals (e.g., at radio frequencies such as microwave ormillimeter wave), employ a heterodyne system to convert a signal fromone frequency to another frequency during signal processing. Forinstance, when a conventional microwave system receives a signal at amicrowave frequency, the system translates the signal from the microwavefrequency to a lower frequency optimized for transmission over a cablemedium. Conventional microwave systems typically perform thistranslation by converting the radio frequency (RF) signal (in this caseat a microwave frequency) to an intermediate frequency (IF) that can bebetter modulated over cable mediums.

FIG. 1 illustrates one such conventional heterodyne system 100configured to convert a radio frequency signal 102 to an intermediatefrequency signal 120. In particular, the heterodyne system 100illustrates a double downconversion heterodyne system, where the radiofrequency signal 102 is first downconverted to a first intermediatefrequency signal 110 for purposes of image filtering, before beingdownconverted to the second intermediate frequency 120 for subsequentsignal processing (e.g., data demodulation and/or carrier recovery). Asillustrated, the conventional heterodyne system 100 performs the doubledownconversion by amplifying the radio frequency signal 102 with anamplifier 104 and then (at a mixer 106) mixing the resulting, amplifiedradio frequency signal with an oscillator signal (at a frequency F₁)generated by a oscillator 108. The mixing results in the firstintermediate frequency signal 110 (IF₁), which is subsequently filteredby a filter 112 (e.g., for image filtering) and amplified by anamplifier 114 before being mixed (at a mixer 116) with an oscillatorsignal (at a frequency F₂) generated by another oscillator 118. From themixer 116, the second intermediate frequency signal 120 is produced.Following further amplification, the second intermediate frequencysignal 120 would be ready for further demodulation and/or carrierrecovery processes.

SUMMARY

Various embodiments provide for systems and methods for signalconversion of one modulated signal to another modulated signal usingdemodulation and then re-modulation.

According to some embodiments, a signal receiving system is providedcomprising an I/Q demodulator, an I/Q signal adjustor, and an I/Qmodulator. The I/Q demodulator may be configured to demodulate the firstmodulated signal to an in-phase (“I”) signal and a quadrature (“Q”)signal based on a first oscillator signal (e.g., at a first frequency),where the first modulated signal is modulated (e.g., at a remotemicrowave site) based on a second oscillator signal (e.g., at or nearthe first frequency) that is asynchronous to the first oscillatorsignal.

As a result of having the first oscillator signal be asynchronous to thesecond oscillator signal upon which the first modulated signal ismodulated, the I/Q demodulator (also referred to herein as the“receive-side I/Q modulator”) is regarded as un-synchronized with thetransmit-side I/Q modulator that is providing/generating the firstmodulated signal. Such a situation may arise in wireless communicationsenvironment (e.g., environment using microwave communications), wherethe I/Q modulator of a wireless transmitter is located at a first siteand the I/Q demodulator of a wireless receiver at a second site remotefrom the first site, where wireless synchronization is difficult orimpractical. Generally, when the receive-side I/Q demodulator is notsynchronized with the transmit-side I/Q modulator, constellation spinresults from the difference between the local oscillator frequency(e.g., of the first oscillator frequency) used by the receiver-side I/Qdemodulator and the local oscillator frequency used by the transmit-sideI/Q modulator (e.g., 0.01 Hz). This constellation spin can lead tonoticeable SNR degradation of modulated signals on the receiver-side.However, various embodiments described herein obviate the need for thereceive-side I/Q demodulator to be synchronized with transmit-side I/Qmodulator so that the receiver-side, downstream SNR degradation isavoided.

The I/Q signal adjustor may be configured to adaptively adjust the Qsignal to increase the signal-to-noise ratio (SNR) of a transitorysignal that is based on the second modulated signal, wherein the Qsignal is adjusted based on a calculated error determined for thetransitory signal. The I/Q modulator may be configured to modulate thesecond modulated signal based on the I signal and the adjusted Q signal.For some embodiments, the I signal may be filtered (e.g., low-passfiltered) and/or otherwise modified before being modulated. Likewise,for some embodiments, the Q signal may be filtered and/or otherwisemodified before or after being adjusted by the I/Q signal adjustor.

Depending on the embodiment, the adaptive adjustment of the Q signal maycomprise applying a quadrature correction to the Q signal, adjusting again (e.g., differential gain) of the Q signal, or both. By adjustingthe Q signal, various embodiments can correct for various types oferrors present in the transitory signal that results from the secondmodulate signal. Examples of errors correctable through the I/Q adjustormay include quadrature error, gain error, delay error, and phaserotation error.

A demodulator downstream (hereafter, referred to as the “downstreamdemodulator”) from the I/Q modulator may subsequently receive the secondmodulated signal as the transitory signal (e.g., where the transitorysignal is identical to or slightly modified in comparison to the secondmodulated signal) and demodulate the transitory signal for furthersignal processing (e.g., to retrieve the carried data). For someembodiments, the downstream demodulator may be configured to demodulatethe transitory signal and to assist in determining the calculated errorfor the transitory signal. For example, based on the demodulation of thetransitory signal, the downstream demodulator may capable of providing amean squared error (MSE) for the transitory signal, which may besubsequently utilized in determined a calculated error for thetransitory signal (e.g., apply an algorithm to the MSE, such as thesteepest decent algorithm). For some embodiments, the signal receivingsystem may further comprise the downstream demodulator.

For some embodiments, the I/Q signal adjustor may be configured toadaptively adjust the I signal and/or adjust the Q signal to increasethe SNR of the transitory signal, where the adjusted I signal and/or theadjusted Q signal is adjusted according to the calculated errordetermined for the transitory signal. Accordingly, the I/Q modulator maybe configured to modulate (i.e., re-modulate) the I and Q signalsresulting from the I/Q signal adjustor to the second modulated signal.For instance, the I/Q signal adjustor may adjust just the I signal, justthe Q signal, or both, and the I/Q modulator would modulate the secondmodulated signal based on those signal adjustments. For someembodiments, the I signal and/or the Q signal may be filtered and/orotherwise modified before or after the adjustment process but before themodulation of the second modulated signal based on the I and Q signalsresulting from the I/Q signal adjustor.

In various embodiments, the signal receiver system is implemented as asplit-mount system, common for microwave systems, where an out-door unit(ODU) comprises the I/Q demodulator, the Q signal adjustor, and the I/Qre-modulator, and where an in-door unit (IDU) is coupled to the ODU andcomprises the downstream demodulator. For some embodiments, thedownstream demodulator may be part of a remote access card (RAC), whichmay be configured to be installed/implemented in an ODU.

In some split-mount embodiments, a radio frequency (RF) signal (e.g.,microwave frequency signal) may be received at the I/Q demodulator ofthe ODU as a first modulated signal. From the I/Q signals of the RFsignal, the I/Q modulator outputs a second modulated signal having amodulated frequency that is lower than that of the RF signal, and havinga modulate frequency that makes the second modulated signal suitable fortransmission over a cable (e.g., over a cable coupling the ODU to theIDU). A signal based on the second modulated (a transitory signal) mayeventually be received by the downstream demodulator of the IDU, and thedownstream demodulator, in turn, will generate the error information(e.g., MSE) for the transitory signal as the transitory signal isdemodulated. This error information may eventually be transmitted backto the ODU as telemetry data, which the ODU translates into adjustmentsto be applied to the I/Q signals of the first modulated signal (e.g., bythe I/Q signal adjustor). Subsequently, the adjusted I/Q signals aremodulated to a newer second modulated signal that is transmitted to theIDU, thereby repeating the correction process.

By providing the error information from the downstream demodulator ofthe IDU to the I/Q signal adjustor of the ODU in this manner, variousembodiments facilitate an error feedback loop by which the ODU cancontinuously adjust the second modulated signals in the ODU for thebenefit of lessening errors in the transitory signal of the IDU.

According to some embodiments, various operations described herein maybe implemented using a digital device and may provide for a computerprogram product comprising a computer useable medium having computerprogram code embodied therein for causing a computing device (i.e., adigital device) to perform specific operations described herein.Embodiments described herein may be utilized in converting (e.g.,downconvert or upconvert) a signal from one frequency to anotherfrequency.

Other features and aspects of various embodiments will become apparentfrom the following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresof the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are provided for purposes of illustration only and merelydepict typical or example embodiments. These drawings are provided tofacilitate the reader's understanding and shall not be consideredlimiting of the breadth, scope, or applicability various embodiments.

FIG. 1 is a diagram illustrating an example of a conventional heterodynesystem used in down conversion of signals.

FIG. 2 is a diagram illustrating an example of a signal receiving systemin accordance with some embodiments.

FIG. 3 is a diagram illustrating an example of a microwavecommunications system in which various embodiments may be implemented orutilized.

FIG. 4 is a diagram illustrating an example of a split-mount system inaccordance with some embodiments.

FIG. 5 is an example of a constellation plot illustrating signal error.

FIG. 6 is an example of a constellation plot resulting from someembodiments.

FIG. 7 is a flowchart illustrating an example of a method for signalmodulation in accordance with some embodiments.

FIG. 8 is a block diagram illustrating an example of a digital devicethat may be utilized by some embodiments.

The figures are not intended to be exhaustive or to limit theembodiments to the precise form disclosed. It should be understood thatvarious embodiments may be practiced with modification and alteration.

DETAILED DESCRIPTION

Various embodiments relate to systems and methods for receiving,demodulating and modulating signals. Some embodiments permit the use ofa receiver-side demodulator/modulator combination (also referred toherein as a “re-modulator”) that lacks synchronization with atransmitter-side modulator that provides the receiver-side re-modulatorwith a modulated signal. The re-modulator may adaptively adjust in-phase(“I”) and/or quadrature (“Q”) signals (e.g., baseband signals)demodulated from the received modulated signal to compensate for thesignal-to-noise (SNR) degradation that would otherwise result from thelack of synchronization.

Adjustments to an in-phase signal and/or quadrature signal may compriseadjustment of differential gain or adjustment to phase difference (e.g.,by way of a quadrature correction). Embodiments may adjust the I and/orQ signals to increase the SNR and decrease the mean-squared error (MSE)of a signal that is demodulated downstream from the re-modulator(hereafter, referred to as the “downstream signal”). The MSE for thedownstream signal may be provided by a demodulator located downstreamfrom the re-modulator. Additionally, an adaptive algorithm (e.g.,steepest decent algorithm) may be applied to the MSE and result incontrol signals that provide adjustments to the I and/or Q signals bythe re-modulator. In particular embodiments, the adaptive algorithm maybe used to continuously provide such control signals to there-modulator, which in turn adjusts the I and/or Q signals for increasedSNR. The adaptive algorithm may be applied or the control signal may beprovided to the re-modulator when the MSE reaches or surpasses aparticular threshold value. Depending on the embodiment, the thresholdvalue may be statically or adaptively determined.

Embodiments may be implemented as a signal receiving system comprisingan I/Q demodulator that demodulates a first modulated signal to anin-phase (“I”) signal and a quadrature (“Q”) signal, an I/Q signaladjustor that adaptively adjusts the Q signal to increase thesignal-to-noise ratio (SNR) of a transitory signal (“downstream signal”)that is based on a second modulated signal, and an I/Q modulator(hereafter, also referred to as the “receiver-side I/Q modulator”) thatmodulates the I signal and the adjusted Q signal to the second modulatedsignal. To increase the SNR, the Q signal may be adjusted based on acalculated error of the downstream signal. The error may be determinedduring processing by a demodulator (e.g., I/Q demodulator) locateddownstream from the receiver-side I/Q modulator.

Errors observed for the transitory signal may be due, in part, toquadrature imbalance, differential delay in the circuit, gain imbalancebetween I and Q signals, or quadrature imbalance in the transmitter-sideI/Q modulator. These imbalances and/or delays may be attributed to theun-synchronization between the local oscillation utilized by the I/Qdemodulator (the receiver-side I/Q modulator) and the local oscillatorutilized by the modulator of the transmitter that is generating thefirst modulated signal (hereafter, referred to as the “transmitter-sideI/Q modulator”). Normally, this un-synchronization, may result inundesirable constellation spin (e.g., for QAM signals) at a rate equalto the difference between the local oscillators; even a slight spin(e.g., 0.01 Hz) may be sufficient enough to create imbalances and/ordelays that result in SNR degradation downstream from the receiver-sideI/Q modulator (i.e., the re-modulator).

However, various embodiments may compensate for the constellation spinstemming from quadrature imbalances, gain imbalances, and/or circuitdelays, to achieve increased SNR. In particular, some embodiments maymitigate SNR performance degradation that would otherwise result fromthe receiver-side I/Q demodulator being not synchronized with thetransmitter-side I/Q modulator, especially in applications where thefirst modulated signal is a high modulation quadrature-amplitudemodulation (QAM) signal. Particular embodiments enable demodulation andthen modulation (i.e., re-modulation) to be utilized in place ofheterodyne downconversion systems, and enable suchdemodulation/re-modulation to be used without need for synchronizationbetween the local oscillator of the receiver-side demodulator and thelocal oscillator of the transmitter-side modulator.

In certain embodiments, the use of demodulation/modulation is cheaperthan use of a heterodyne downconverter, as demodulation/modulation canbe implemented using components (e.g., synthesizers and modulationcomponents) having a lower cost than those of a traditional heterodynedownconversion system. Additionally, the use of demodulation/modulationcan offer a less costly approach to intermediate frequency (IF)filtering by enabling replacement of higher cost ceramic filtering downwith lower cost filtering of in-phase and quadrature signals (e.g.,baseband signals).

The equations that follow are useful in explaining the operation andbehavior of some embodiments. The equations are defined according to thefollowing terms.

θ=demodulator quadrature error

ϕ=demodulator rotation error

α=re-modulator quadrature error

g=demodulator to re-modulator baseband gain error

Δω=frequency error between I/Q modulator oscillator and demodulatoroscillator.

ω₀=IF frequency of s(t)

ω₁=IF frequency of y(t)

I=Modulator I channel on TX side

Q=Modulator Q channel on TX side

Equation 1 may describe a transmitter-side modulator that produces anideal signal S(t) at IF frequency ω₀.S(t)=I*Cos(ω₀ t)+Q*Sin(ω₀ t)  Equation 1

Equations 2 and 3, as recited below, may describe a receiver-side I/Qdemodulator of an embodiment, which is configured to produce ademodulated in-phase signal (Id) and a demodulated quadrature signal(Qd) from the signal S(t) received by the receiver-side I/Q demodulatorfrom the transmitter-side modulator. In accordance with someembodiments, the signal S(t) may be received by the receiver-side I/Qdemodulator as a radio frequency (RF) signal (e.g., a QAM signal at amicrowave frequency). The signals Id and Qd may not be exact replicas ofthe signals I and Q received by the transmitter-side modulator (See,Equation 1).Id=S(t)*Cos(ω₀ t+Δωt+ϕ+θ/2),  Equation 2Qd=S(t)*Sin(ω₀ t+Δωt+ϕ−θ/2)  Equation 3

After multiplying and filtering higher order frequency terms ofEquations 2 and 3 (the ones that occur at 2*ω₀), the followingrelationships may result:Id=*Cos(Δωt+ϕ+θ/2)−Q*Sin(Δωt+ϕ+θ/2),  Equation 4Qd=Q*Cos(Δωt+−θ/2)+I*Sin(Δωt+ϕ−θ/2)  Equation 5

For Equations 4 and 5, the term Δω may describe the constellation spinthat results from the receiver-side I/Q demodulator being notsynchronized with the transmitter-side modulator. As noted herein, suchspin can be a source of error and SNR degradation in demodulatorsdownstream from the receiver-side I/Q modulator of some embodiments(described below by Equations 6 and 7). Generally, when there is noconstellation spinning, the constellation may be considered stable butmay still be rotated by ϕ. When the constellation is spinning but thereare no quadrature and gain errors, then demodulation downstream from thereceiver-side I/Q modulator may not be affected by the spinning.However, when there is constellation spinning as well as quadratureand/or gain errors, SNR degradation result in downstream demodulators.

Equation 6, as recited below, may describe the receiver-side I/Qmodulator of an embodiment, which generates a new signal, the signalY(t) at a different intermediate frequency.Y(t)=g*Id*Cos(ω₁ t+α/2)+Qd*Sin(ω₁ t−α/2)  Equation 6

Multiplying out the signal Y(t) in Equation 6 may result in Equation 7.Y(t)=I{g[Cos(ω₁ t−Δωt−ϕ+α/2−θ/2)+Cos(ω₁ t+Δωt+ϕ+α/2+θ/2)]+Cos(ω₁t−Δωt−ϕ−α/2+θ/2)−Cos(ω₁ t+Δωt+ϕ−α/2−θ/2)}+Q{g[Sin(ω₁t−Δωt−ϕ+α/2−θ/2)−Sin(ω₁ t+Δωt+ϕ+α/2+θ/2)]+Sin(ω₁ t−Δωt−ϕ−α/2+θ/2)−Sin(ω₁t+Δωt+ϕ−α/2−θ/2)}  Equation 7

Equations 8 and 9, as recited below, may describe the downstreamdemodulator and carrier recovery, which produces the signals Ir and Qrfrom the signal Y(t) produced by the receiver-side I/Q modulator (See,Equations 6 and 7). As shown by Equations 8 and 9, demodulation of thesignal Y(t) to the signals Ir and Qr may accomplished by multiplyingY(t) by Cos(ω₁t−Δωt−ϕ) and Sin(ω₁t−Δωt−ϕ) respectively. By demodulatingin accordance with Equations 8 and 9, various embodiments can determineerrors within the signal Y(t) (e.g., quadrature and/or phase rotationerrors) that result in SNR degradation.Ir=I{Cos(α/2−θ/2)*(1+g)+g*Cos(2*Δωt+2*ϕ+α/2+θ/2)−Cos(2*Δωt+2*ϕ−α/2−θ/2)}+Q{Sin(α/2−θ/2)*(g−1)−g*Sin(2*Δωt+2*ϕ+α/2+θ/2)+Sin(2*Δωt+2*ϕ−α/2−θ/2),  Equation8Qr=Q{Cos(α/2−θ/2)*(1+g)−g*Cos(2*Δωt+2*ϕ+α/2+θ/2)+Cos(2*Δωt+2*ϕ−α/2−θ/2)}+I{Sin(α/2−θ/2)*(1−g)−g*Sin(2*Δωt+2*ϕ+α/2+θ/2)+Sin(2*Δωt+2*ϕ−α/2−θ/2)}  Equation9

As described herein, based on the determined errors, certain embodimentsadjust the signal Id or the signal Qd in Equation 7 to mitigate thosedetermined errors. For instance, systems and methods described hereinmay apply a quadrature correction (e.g., resulting in an adjustment toα) and/or a gain adjustment to the signal Id signal or the signal Qd(e.g., resulting an adjustment to g of 0.9 or 1.1).

FIG. 2 is a diagram illustrating an example of a signal receiving system200 in accordance with some embodiments. In addition to applicationsrelating to wired and wireless communication systems, the illustratedsystem 200 may be implemented for electronic applications where signalprocessing is utilized, such as video processing or audio processing. Asshown, the signal receiving system 200 comprises amplifiers 204 and 216,a downconversion re-modulator 208 coupled to local oscillators 210 and212, a demodulator 218 downstream from the downconversion re-modulator208, and an error module 220 coupled to the demodulator 218. The system200 may begin at the amplifier 204, where an input signal 202 isreceived for downconversion. In the contexts of wireless communications,the input signal 200 may be a radio frequency (RF) signal (e.g., atmicrowave frequency) received by via an RF antenna coupled to theamplifier 204. The amplifier 204 may amplify the input signal 200 andprovide the resulting signal as a first modulated signal 206

The downconversion re-modulator 208 may be configured to downconvert thefirst modulate signal 206 (e.g., the input signal 202 as provided by theamplifier 204) to a second modulated signal 214, without requiringsynchronization with the transmitter that provided the first modulatedsignal.

By way of example, the downconversion re-modulator 208 may receive thefirst modulated signal from the amplifier 204 and demodulate the firstmodulated signal 206 to an in-phase (“I”) signal and a quadrature (“Q”)signal based on a first oscillator signal at frequency F₁ from the localoscillator 208. As discussed below, The first oscillator signal may beun-synchronized with the oscillator signal used in the modulation of thefirst modulated signal. Subsequently, the downconversion re-modulator208 may be adaptively adjust the Q signal to increase thesignal-to-noise ratio (SNR) for a transitory signal that is based on thesecond modulated signal 214 outputted by the downconversion re-modulator208.

For some embodiments, the downconversion re-modulator 208 may adjust theQ signal based on a calculated error 222 provided in response todemodulation of the transitory signal by a demodulator downstream fromthe downconversion re-modulator 208. In one example, the demodulator 218may receive (as the transitory signal) an amplified signal from theamplifier 216 based on the second modulated signal 214, and demodulatesto data signal(s) 224 (e.g., I and Q signals). As a result of thedemodulation, the demodulator 218 may provide error data regarding thetransitory signal to the error module 220. The error module 220, inturn, may apply an adaptive function (e.g., steepest decent algorithm)to the provided error data and generate the calculated error 222 inresponse. In doing so, the demodulator 218 and the error module 220enable the downconversion with re-modulator 208 to adjust the I signaland/or the Q signal downstream error feedback.

In performing various operations, the downconversion re-modulator 208may comprise an I/Q modulator, an I/Q demodulator, and componentsoperable in adjusting an I signal, a Q signal, or both. Components thatfacilitate adjustment of the I signal and/or the Q signal may includefilters (e.g., low pass filters), multiplier(s), variable gainamplifier, cross taps, and the like. More with respect to these circuitsand components are further described below with regard to FIG. 4.

Those skilled in the art will appreciate that for certain embodiments,the downconversion re-modulator 208 may be replaced by an alternativere-modulator that performs upconversion or performs some combination ofboth upconversion and downconversion. Additionally, in accordance withsome embodiments, the use of two local oscillators (210, 212), asillustrated in FIG. 2, may enable the downconversion re-modulator 208 toreplace one or two downconverters of a traditional double downconversionheterodyne system (e.g., downconversion to frequency F₁ anddownconversion to frequency F₂).

Though the FIG. 2 illustrates the downconversion re-modulator 208 beingcoupled to two local oscillators, those skilled in the art willappreciate that various embodiments may have more or less oscillatorscoupled to the re-modulator. For example, the downconversionre-modulator 208 may be coupled to a single local oscillator.

FIG. 3 is a diagram illustrating an example of a microwavecommunications system 300 in which various embodiments may beimplemented or utilized. As shown, the exemplary microwavecommunications system 300 is a split-mount wireless system comprisingindoor units (IDU) 306 and 324, outdoor units (ODU) 312 and 320, andantennas 314 and 318 at each of two communications sites 302 and 330.Each of the IDUs 305 and 324 may comprise a radio access card (RAC) 308,326 respectively configured to communicatively couple the IDUs to therespective ODU 312, 320 (e.g., via cables 310 and 322). In FIG. 3, themicrowave communications system 300 facilitates communications between anetwork 304 and a network 328.

The IDUs 306 and 324 may function as the signal processing units for themicrowave communications system 300. Generally, locating the signalprocessing equipment in the IDU helps minimize the amount of equipmentthat has to be located in the ODUs 312 and 320. For some embodiments,each of the IDUs 306 and 324 comprises a digital signal processormodule, a combiner/splitter module, a modem module, a power supplymodules, and possibly auxiliary components/modules (e.g., forredundancy). The ODUs 312 and 320 and/or IDUs 306 and 324 may utilizewaveguides and/or waveguide filters to implement their particularfunctionalities.

As illustrated, the IDUs 306 and 324 are coupled to the ODUs 312 and320. The ODUs may function as the radio frequency units for themicrowave communications system 300 and, as such, may comprise theintermediate frequency (IF) and radio frequency (RF) equipment needed totransmit and receive wireless signals over a wireless channel. Forexample, each of the ODUs 312 and 320 may comprise two or moretransceivers modules, and a transducer module that connects to theantenna (314 and 318). Generally, the ODUs 312 and 320 are responsiblefor converting the data stream (e.g., binary data or analog signal) fromthe IDUs 306 and 324 into corresponding wireless signal(s) to betransmitted via the antennas 314 and 318, and converting wirelesssignal(s) received via the antennas 314 and 318 into a correspondingdata stream (e.g., binary data or analog signal) to be processed by theIDUs 306 and 324. As noted herein, the antennas 314 and 318 may beconfigured to transmit and receive wireless signals.

While the embodiments described in FIG. 3 are described in the contextof a microwave transmission system, some embodiments may be implementedin other wireless communications system, including indoor-only systems,and cellular phone systems, WiFi systems, and the like.

FIG. 4 is a diagram illustrating an example of a split-mount system 400in accordance with some embodiments. As shown, the split-mount system400 may comprise the out-door-unit (ODU) 320 and the in-door unit (IDU)324 coupled to the ODU 320 via the cable 322. In accordance with FIG. 3,the ODU 320 may be coupled to the antenna 318, which receives a radiofrequency (RF) signal (e.g., communication 316) from a system at site A302 and delivers the RF signal to the ODU 320. On the other end, the IDU324 may be coupled to the communications network 328, and is generallyconfigured to provide data from the RF signal to the network 328.

As illustrated in FIG. 4, the ODU 320 may comprise an I/Q demodulator404, local oscillators 406 and 424, low-pass filters 412 and 414, avariable gain amplifier (VGA) 416, a multiplier 418, a cross-tap 420, anI/Q modulator 422, a N-plexer 428, a telemetry receiver 432, anddigital-to-analog converters (DACs) 434 and 436. The IDU 324 maycomprise an N-plexer 442, a demodulator 444, a MSE module 450, and atelemetry transmitter 454, some or all of which may be part of theremote access card (RAC) disposed in the IDU 324. In the ODU 320, theI/Q demodulator 404, the low-pass filters 412 and 414, the variable gainamplifier (VGA) 416, the multiplier 418, the cross-tap 420, and the I/Qmodulator 422 may constitute the re-modulator for certain embodiments,which may not be synchronized with the transmitter that provides the RFsignal 402. In the IDU 324, the demodulator 444 may constitute thedownstream demodulator that provided error feedback to the re-modulatorfor I/Q signal adjustment purposes.

In accordance with some embodiments, a radio frequency (RF) signal 402,received via an antenna coupled to the ODU 320, may be provided to theI/Q demodulator 404 for demodulation into an in-phase signal (Id) 408 aand a quadrature signal (Qd) 410 a at a local oscillation frequency F₁(generated by the local oscillator 406). Depending on the embodiment,the in-phase signal (Id) 408 a and the quadrature signal (Qd) 410 a maybe considered baseband signals of the RF signal 402. Followingdemodulation, the in-phase signal (Id) 408 a and the quadrature signal(Qd) 410 a may be filtered for undesired signals before furtherprocessing, thereby resulting in a filtered in-phase signal (Id′) 408 band a filtered quadrature signal (Qd′) 410 b.

To increase downstream SNR in the IDU 324, the filtered quadraturesignal (Qd′) 410 b may be adjusted by way of the variable gain amplifier(VGA) 416 and/or the multiplier 418 and the cross-tap 420 disposedbetween the I/Q demodulator 404 and the I/Q modulator 422. While the VGA416 may control the differential gain between the filtered in-phasesignal (Id′) 408 b and the filtered quadrature signal (Qd′) 410 b, themultiplier 418 and the cross-tap 420 may control the quadrature error bymultiplying the filtered in-phase signal (Id′) 408 b to the filteredquadrature signal (Qd′) 410 b. Since the multiplying coefficient may bea positive (+) or negative (−) voltage, the multiplier 418 may be a4-quadrant multiplier.

Though FIG. 4 depicts both the differential gain and the quadratureerror of the system 400 being controlled through adjustment of thefiltered quadrature signal (Qd′) 410 b to adjusted quadrature signal(Qd″) 410 c, those skilled in the art will appreciate that someembodiments may adjust the filtered in-phase signal (Id′) 408 b inaddition to or in place of adjusting the filtered quadrature signal(Qd′) 410 b. Additionally, those skilled in the art will also appreciatethat embodiments may employ different methods of I/Q signal adjustmentwhen controlling errors that result from the in-phase signal (Id) 408 aand/or the quadrature signal (Qd) 410 a. Furthermore, notwithstandingadjustments to the filtered in-phase signal (Id′) 408 b and/or thefiltered quadrature signal (Qd′) 410 b for purposes of increasingdownstream SNR, various embodiments may filter and/or otherwise modifythe in-phase signal (Id) 408 a and/or the quadrature signal (Qd) 410 ain a different manner and different order (e.g., filter afteradjustment) than what is illustrated for the system 400.

Thereafter, the I/Q modulator 422 may modulate, as the second modulatedsignal, an intermediate frequency (IF) signal 426 based on the filteredin-phase signal (Id′) 408 b, the adjusted quadrature signal (Qd″) 410 c,and a oscillator signal generated by the local oscillator 424 at afrequency F₂. For some embodiments, the frequency F₂ may be such thatthe IF signal 426 is suitable for transmission over the cable 322 (e.g.,600 MHz), so as to reduce cable loss. Eventually, the resulting IFsignal 426 may be routed from the ODU 320 to the IDU 324, through theN-plexer 428, and over the cable 322.

Eventually, the demodulator 444 may receive the intermediate frequency(IF) signal 426, as a downstream modulated signal, through the N-plexer442 and over the cable 422. The demodulator 444, in turn, demodulatesthe IF signal 426 into data signal(s) 446. For example, the datasignal(s) 446 may comprise I and Q signals which a modem or other device(e.g., disposed in the IDU 324) can translate into data signals for anetwork connection (e.g., to the network 328). According to someembodiments, the demodulator 444 may be configured to provide errorinformation, such as mean-squared error (MSE) 448, from the demodulationprocess, where the error information relates to the IF signal 426. Asillustrated, the MSE module 450 may apply an algorithm to the MSE 448received from the demodulator 444 and output a calculated error 452 thatcan be utilized by the ODU 320 in its adjustment of the filteredquadrature signal (Qd′) 410 b.

According to some embodiments, the calculated error 452 may betransmitted from the IDU 324 to the ODU 320 as telemetry data 456, viathe telemetry transmitter 454, the N-plexer 442, and then over the cable422. The telemetry data transmitted from the IDU 324 to the ODU 320could include information other than the calculated error 452 including,for example, settings for the ODU 320 and information regarding thecurrent status of the IDU 320. The telemetry data 456 may be transmittedfrom the IDU 324 to the ODU 320 over the cable 322 using frequency-shiftkeying (FSK) modulation. For some embodiments, the telemetry data 456may be transmitted from the IDU 324 to the ODU 320 over the cable 322 ata signal frequency between approximately 4 MHz and 5 MHz.

The ODU 320 may receive the telemetry data 456 from the IDU 324, at thetelemetry receiver 432, as the telemetry data 430. From the receivedtelemetry data 430, the telemetry receiver 432 may be configured toextract one analog signal that can be converted to a quadraturecorrection digital control signal 438, and another analog signal thatcan be converted to a differential gain digital control signal 440. Inaccordance with various embodiments, the digital-to-analog converters(DACs) 434 and 436 may facilitate conversion of the analog signalsextracted from the telemetry data 430 to the digital control signal 438for quadrature correction 438, and the digital control signal 440 fordifferential gain. The multiplier 418 may apply adjustments to thefiltered quadrature signal (Qd′) 410 b according to the quadraturecorrection digital control signal. Similarly, the variable gainamplifier (VGA) 416 may apply a differential gain to the filteredquadrature signal (Qd′) 410 b according to the differential gain digitalcontrol signal 440.

FIG. 5 is an example of a constellation plot 500 illustrating signalerror. In particular, the constellation plot 500 illustrates thedemodulation results of a signal before the I and Q signals are adjusted(e.g., gain adjustment and/or quadrature correction) in accordance withsome embodiments. The results of the constellation plot 500 are based onone or more quadrature, phase, gain, and carrier rotation errorsexisting in the pre-adjusted I and Q signals. The constellation plot 500exhibits a SNR of 29.6 dB due to the I/Q signal impairments. Thespinning results in the outer points of the constellation formingcircles generally reduce the SNR performance downstream from are-modulator that is not synchronized with a transmitter that isproviding it with a modulated signal.

In contrast, FIG. 6 provides a constellation plot 600 illustrating thedemodulation results of the same signal but after the I and Q signalsare adaptively adjusted, in accordance with some embodiments, toincrease downstream SNR. The constellation plot 600 exhibits a SNR of 39dB.

FIG. 7 is a flowchart 700 illustrating an example of a method for signalmodulation in accordance with some embodiments. For certain embodiments,the exemplary method illustrated may be operable with the system 200 ofFIG. 2 and/or the split-mount system 400 of FIG. 4. For example, withrespect to the split-mount system 400 of FIG. 4, the method may begin atoperation 702 with the I/Q demodulator 404 receiving the radio frequency(RF) signal 402 as a first modulate signal and the I/Q demodulator 404demodulating the RF signal 402 to the in-phase signal (Id) 408 a and thequadrature signal (Qd) 410 a. As described herein, the RF signal 402 maybe received by way of an antenna configured to receive signals atparticular radio frequencies (e.g., microwave or millimeter wavefrequencies). As illustrated in FIG. 4, each of the in-phase signal (Id)408 a and the quadrature signal (Qd) 410 a may be respectively filteredby the low-pass filters 412 and 414, thereby resulting in the filteredin-phase signal (Id′) 408 b and the filtered quadrature signal (Qd′) 410b, respectively.

At operation 704, the filtered quadrature signal (Qd′) 410 b may beadjusted based on the calculated error provided by a downstreammodulated signal from the demodulator 444. For example, during operation704, the variable gain amplifier (VGA) 416 may be utilized to adjust thedifferential gain of the filtered quadrature signal (Qd′) 410 b and/orthe multiplier 418 and the cross-tap 420 may utilized to apply aquadrature correction the filtered quadrature signal (Qd′) 410 b. Suchadjustments may be facilitated by the calculated error being transmittedfrom the IDU 324 to the ODU 320 as telemetry data (e.g., via thetelemetry transmitter 454 and the telemetry receiver 432), and the ODU320 extracting the quadrature correction control signal 438 and/or thedifferential gain control signal 440 from the received telemetry data(e.g., via the telemetry receiver 432).

Those skilled in the art will appreciate that various embodiments arenot limited to the components or the component arrangement shown in thesignal path between the I/Q demodulator 404 and the I/Q modulator 422.As such, the filtered in-phase signal (Id′) 408 b may be adjusted basedon the calculated error, and that such adjustment may be in place or inaddition to the adjustment of the filtered quadrature signal (Qd′) 410 bshown in FIG. 4. Additionally, depending on the embodiment, the in-phasesignal and/or quadrature signal may be filtered and/or otherwisemodified before either is adjusted to increase downstream signal SNR.

At operation 706, the intermediate frequency (IF) signal 426 may bemodulated as a second modulated signal, based on the filtered in-phasesignal (Id′) 408 b and the adjusted quadrature signal (Qd″) 410 c, bythe I/Q modulator 422. As shown in FIG. 4, the in-phase signal (Id) 408a may be filtered by the low-pass filter 412 to the in-phase signal(Id′) 408 b before being received by the I/Q modulator 422 formodulation.

At operation 708, the demodulator 444 located downstream with respect tothe I/Q modulator 422 may receive a downstream modulated signal based onthe intermediate frequency (IF) signal 426 (e.g., the second modulatedsignal) and demodulate the downstream modulated signal to one or moredata signals (e.g., I and Q signals for interpretation by a modemcoupled to the demodulator 444).

At operation 710, the demodulator 444 in combination with the MSE module450 may calculate the error 452 to be used in adjusting the filteredquadrature signal (Qd′) 410 b to adjusted quadrature (Qd″) 410 c.Depending on the embodiment, the calculated error 452 may be determinedbefore, during, or after the demodulation of the downstream modulatedsignal. As noted herein, the MSE module 450 may be configured to applyof an adaptive algorithm, such as steepest decent, to the mean-squarederror (MSE) information provided by the demodulator 444 in response tothe demodulation of the downstream modulated signal. For someembodiments, subsequent to operation 710, the method may return tooperation 704 where the filtered quadrature signal (Qd′) 410 b may beadjusted based on the calculated error 450 determined at operation 710.

As depicted in FIG. 4, to facilitate the adjustment of the filteredquadrature signal (Qd′) 410 b, the calculated error 452 may betransmitted to from the IDU 324 to the ODU 320, via the telemetrytransmitter 454 and the telemetry receiver 432, in the telemetry data456 to the ODU. According to some embodiments, the telemetry data 456may be transmitted from the IDU 324 to the ODU 320 over the cable 322 asinformation encoded using frequency-shift keying (FSK) modulation. Forsome embodiments, the telemetry data 456 may be transmitted from the IDU324 to the ODU 320 at a signal frequency between approximately 4 MHz and5 MHz.

Those skilled in the art would appreciate that one or more operations ofmethod as illustrated in FIG. 7 could be performed in the context ofother systems or components.

As used herein, the term module might describe a given unit offunctionality that can be performed in accordance with one or moreembodiments. As used herein, a module might be implemented utilizing anyform of hardware, software, or a combination thereof. For example, oneor more processors, controllers, ASICs, PLAs, PALs, CPLDs, FPGAs,logical components, software routines or other mechanisms might beimplemented to make up a module. In implementation, the various modulesdescribed herein might be implemented as discrete modules or thefunctions and features described can be shared in part or in total amongone or more modules. Even though various features or elements offunctionality may be individually described or claimed as separatemodules, one of ordinary skill in the art will understand that thesefeatures and functionality can be shared among one or more commonsoftware and hardware elements, and such description shall not requireor imply that separate hardware or software components are used toimplement such features or functionality.

Where components or modules of some embodiments are implemented in wholeor in part using software, in some embodiments, these software elementscan be implemented to operate with a digital device capable of carryingout the functionality described with respect thereto. An example of adigital device is shown in FIG. 8. After reading this description, itwill become apparent to one skilled in the art how to implement variousembodiments using other digital devices or architectures.

FIG. 8 is a block diagram of an exemplary digital device 800. Thedigital device 800 comprises a processor 802, a memory system 804, astorage system 806, a communication network interface 808, an I/Ointerface 810, and a display interface 812 communicatively coupled to abus 814. The processor 802 may be configured to execute executableinstructions (e.g., programs). In some embodiments, the processor 802comprises circuitry or any processor capable of processing theexecutable instructions.

The memory system 804 is any memory configured to store data. Someexamples of the memory system 804 are storage devices, such as RAM orROM. The memory system 804 can comprise the ram cache. In variousembodiments, data is stored within the memory system 804. The datawithin the memory system 804 may be cleared or ultimately transferred tothe storage system 806.

The storage system 806 is any storage configured to retrieve and storedata. Some examples of the storage system 806 are flash drives, harddrives, optical drives, and/or magnetic tape. In some embodiments, thedigital device 800 includes a memory system 804 in the form of RAM and astorage system 806 in the form of flash data. Both the memory system 804and the storage system 806 comprise computer readable media which maystore instructions or programs that are executable by a computerprocessor including the processor 802.

The communication network interface (com. network interface) 808 can becoupled to a data network (e.g., data network 504 or 514) via the link816. The communication network interface 808 may support communicationover an Ethernet connection, a serial connection, a parallel connection,or an ATA connection, for example. The communication network interface808 may also support wireless communication (e.g., 802.11 a/b/g/n,WiMax). It will be apparent to those skilled in the art that thecommunication network interface 808 can support many wired and wirelessstandards.

The optional input/output (I/O) interface 810 is any device thatreceives input from the user and output data. The optional displayinterface 812 is any device that may be configured to output graphicsand data to a display. In one example, the display interface 812 is agraphics adapter.

It will be appreciated by those skilled in the art that the hardwareelements of the digital device 800 are not limited to those depicted inFIG. 8. A digital device 800 may comprise more or less hardware elementsthan those depicted. Further, hardware elements may share functionalityand still be within various embodiments described herein. In oneexample, encoding and/or decoding may be performed by the processor 802and/or a co-processor located on a GPU.

The above-described functions and components can be comprised ofinstructions that are stored on a storage medium such as a computerreadable medium. The instructions can be retrieved and executed by aprocessor. Some examples of instructions are software, program code, andfirmware. Some examples of storage medium are memory devices, tape,disks, integrated circuits, and servers. The instructions areoperational when executed by the processor to direct the processor tooperate in accord with some embodiments. Those skilled in the art arefamiliar with instructions, processor(s), and storage medium.

The invention claimed is:
 1. A signal receiving system comprising: adownstream demodulator configured to demodulate a first transitorysignal and provide error data of the first transitory signal, the firsttransitory signal being generated from a first quadrature amplitudemodulated (QAM) signal received from a transmitter that used atransmitter oscillator to generate the first QAM signal; an algorithmconfigured to calculate gain error information and quadrature errorinformation based on the error data of the first transitory signal; anI/Q signal adjuster; and a telemetry transmitter configured to transmitthe gain error information and the quadrature error information to theI/Q signal adjuster, the I/Q signal adjuster being configured toadaptively adjust a gain of a future in-phase (“I”) signal or a futurequadrature (“Q”) signal based on the gain error information and toadaptively adjust a quadrature imbalance of the future I signal or thefuture Q signal based on the quadrature error information to increase asignal-to-noise ratio (SNR) of a future transitory signal, the futuretransitory signal being based on the future I signal and the future Qsignal as adjusted.
 2. The signal receiving system of claim 1, furthercomprising a radio antenna configured to receive the first QAM signalfrom the transmitter.
 3. The signal receiving system of claim 1, furthercomprising: a first I/Q demodulator configured to demodulate a futureQAM signal to the future I signal and the future Q signal, the first I/Qdemodulator using a demodulator oscillator that is not synchronized withthe transmitter oscillator; and an I/Q re-modulator configured tore-modulate the future I and Q signals as adjusted to generate thefuture transitory signal.
 4. The signal receiving system of claim 3,wherein the receiver system comprises an out-door unit (ODU), and theODU comprises the I/Q signal adjuster, the first I/Q demodulator, andthe I/Q re-modulator.
 5. The signal receiving system of claim 1, whereinthe receiver system comprises an in-door unit (IDU), and the IDUcomprises the downstream demodulator.
 6. The signal receiving system ofclaim 1, wherein the downstream demodulator is further configured todemodulate the first transitory signal to a data signal.
 7. The signalreceiving system of claim 1, wherein the algorithm is configured tocalculate the gain error information using a steepest descent algorithm.8. The signal receiving system of claim 1, wherein the algorithm isconfigured to calculate the quadrature error information using asteepest descent algorithm.
 9. The signal receiving system of claim 1,wherein the telemetry transmitter is further configured to transmit thegain error information and the quadrature error information to the I/Qsignal adjuster as telemetry data.
 10. The signal receiving system ofclaim 1, wherein the error data comprises mean squared errorinformation.
 11. A method comprising: receiving a first quadratureamplitude modulated (QAM) signal from a transmitter that used atransmitter oscillator to generate the first QAM signal; demodulating afirst transitory signal, the first transitory signal being generatedfrom the first QAM signal; generating error data of the first transitorysignal; calculating gain error information and quadrature errorinformation based on the error data of the first transitory signal;transmitting the gain error information and the quadrature errorinformation to an I/Q signal adjuster; using the I/Q signal adjuster toadaptively adjust a gain of a future in-phase (“I”) signal or a futurequadrature (“Q”) signal based on the gain error information to increasea signal-to-noise ratio (SNR) of a future transitory signal; using theI/Q signal adjuster to adaptively adjust a quadrature imbalance of thefuture I signal or the future Q signal based on the quadrature errorinformation to increase the SNR of the future transitory signal; andusing the future I signal and the future Q signal as adjusted togenerate the future transitory signal.
 12. The method of claim 11,further comprising: demodulating a future QAM signal to the future Isignal and the future Q signal using a first I/Q demodulator, the firstI/Q demodulator using a demodulator oscillator that is not synchronizedwith the transmitter oscillator; and re-modulating the future I and Qsignals as adjusted to generate the future transitory signal.
 13. Themethod of claim 11, wherein the steps of receiving the first QAM signal,using the I/Q signal adjuster to adaptively adjust the gain, using theI/Q signal adjuster to adaptively adjust the quadrature imbalance, andusing the future I signal and the future Q signal as adjusted togenerate the future transitory signal are performed by modules within anout-door unit (ODU).
 14. The method of claim 11, wherein the steps ofdemodulating the first transitory signal, generating the error data,calculating the gain error information and the quadrature errorinformation, and transmitting the gain error information and thequadrature error information to the I/Q signal adjuster are performed bymodules within an in-door unit (IDU).
 15. The method of claim 11,wherein the step of demodulating the first transitory signal includesdemodulating the first transitory signal to a data signal.
 16. Themethod of claim 11, wherein the step of calculating the gain errorinformation and the quadrature error information based on the error dataincludes calculating the gain error information using a steepest descentalgorithm.
 17. The method of claim 11, wherein the step of calculatingthe gain error information and the quadrature error information based onthe error data includes calculating the quadrature error informationusing a steepest descent algorithm.
 18. The method of claim 11, whereinthe step of transmitting the gain error information and the quadratureerror information to the I/Q signal adjuster comprises transmitting thegain error information and the quadrature error information to the I/Qsignal adjuster as telemetry data.
 19. The method of claim 11, whereinthe error data comprises mean squared error information.